Since the mid 1970's, automobiles and other vehicles have had environmental controls installed to reduce the levels of pollutants released into the air. Many states now monitor the levels of emissions from vehicles to ensure that environmental standards are being met. Although testing devices, such as the type disclosed in U.S. Pat. No. 4,175,427 to Blanke, are helpful in monitoring pollutants, one important device, the catalytic converter can not readily be tested, although an accepted test has been developed. This test uses four output gasses to determine the effectiveness of the engine and the pollution controls.
The Blanke Patent discusses the primary reason that catalytic converter tests aren't done: in order to perform the test, the vehicle's engine must be adjusted and then reset. Although the Blanke patent discussed this problem, it states that it is beyond the scope of his disclosure.
To understand the procedure for testing a catalytic converter, it is necessary to discuss what a typical engine does. Theoretically, if gasoline is burned completely with oxygen (O.sub.2) in an internal combustion engine, the products produced by the combustion are water vapor and carbon dioxide (CO.sub.2). In fact, the theoretical products are never fully produced because engines do not usually run at their peak efficiency. Typically, an engine usually produces a mix of carbon monoxide (CO), CO.sub.2, O.sub.2, various hydrocarbon gases, and water vapor. Depending on the operating performance of any given engines, the percentage output of the four gases (CO, CO.sub.2, O.sub.2, and hydrocarbons) can vary considerably. Under ideal conditions, however, an engine operting at peak efficiency with a working catalytic converter will reduce O.sub.2 and CO output because these gases will be combined into additional CO.sub.2. CO.sub.2 output will be maximized and residual hydrocarbon output should be near zero. If CO.sub.2 output is maximized, O.sub.2 output is minimized and hydrocarbons are eliminated, a catalytic converter passing gretaer than 0.5% CO is defective. This test will show proper results only if CO.sub.2 production exceeds 13.6% and O.sub.2 output is slightly above 1.0% (typically 1.2-1.6%). At this level of performance, residual hydrocarbons are reduced to a minimum. A complete discussion of this theory and application can be found in the report MGA-90 by Sun Electric Corporation; the California Bureau of Automotive Repair memorandum dated June 10, 1985; and Catalytic Convertor Test Proposal, Municipality of Anchorage, Vehicle Inspection Program.
In order to achieve the output levels needed to ensure a proper test, the fuel air mixture feeding an engine must be adjusted to either lean or rich, as needed, until the output of the engine matches the test criteria. In all late model vehicles, this cannot be done without adjusting the carburetor or injection system. Recent car models have factory sealed adjustment screws making these adjustment difficult and problematic. Once these adjustment screws are adjusted, they must be precisely reset in order to ensure proper engine performance. Because this is a time consuming and skillful procedure, it is not practical to use this method to test catalytic converters with present day equipment.